An Etymological Dictionary of the German Language/Annotated/sauer
sauer, adjective, ‘sour, acid, bitter,’ from the equivalent Middle High German and Old High German sûr, adjective; corresponding to Dutch zuur, Middle Low German and Anglo-Saxon sûr, English sour, Old Icelandic súrr; Gothic sûrais by chance not recorded. Pre-Teutonic *sûró-s is further attested by Old Slovenian syrŭ, ‘raw,’ and Lithuanian sū́ras, ‘salty.’ Perhaps Greek ξὺρός, ‘sour’ (in Hesych.), and the root ἕυ, ‘to scrape, scratch,’ are also allied; in that case sauer would mean ‘scratching.’ From Teutonic is derived French sur, ‘sour.’